Uh...that's 15x faster than a hard disk...
I was at JPL working in the control room for the Magellan Spacecraft. The actual data rates (X-band) were 268.8 or 115 kbps. Remember data rate from a satellite is usually posted in Bits/sec since data is serially downlinked. One other interesting fact was that the same dish antenna used to collect the SAR data was the same one used to transmit the data back to earth. The following is a brief synopsis of how telemetry is sent from a spacecraft back to the ground.
First what is telemetry?: Telemetry is the process of conveying information by transmitting information from one point to another. The Merriam-Webster dictionary term for telemeter is “transmit (as the measurement of a quantity) by telemeter”. In other words it is a process of conveying information, such as voltages and temperatures, from a remote location to another for subsequent data analysis or interpretation.
On the average spacecraft (I should give a distinction here, spacecraft are either manned or are no longer orbiting the earth, such as an interplanetary, and satellites are unmanned earth orbiters) there are hundreds, possibly even thousands of individual items (including mission data) that need to be transmitted from the vehicle to a ground station for analysis such as a voltage, temperature, attitude and the like.
It is impractical if not downright impossible to simultaneously transmit all of this data to a ground station. So the data is ”injected” into a serial telemetry stream that only requires one (or possibly a few) links between the vehicle and the ground. This process of inserting all of this data in a specific pre-determined pattern is called commutation.
To do this, the data must be digitized (i.e. converted to ones (1s) and zeros (0s). Due to fidelity reasons, link margin, and communications bandwidth, many of these parameters are sent down as an 8 bit (8 serial 1s and 0s) "word". Without going into the math here, this converts into 0 thru 255 decimal or the number 0 thru FF in hex. Usually these values are called Engineering Units (EUs).
If all data is lost, the number either reverts to 0 or 255, which usually is an out-of-limit condition.
All the telemetry monitors are "gathered" as digital words and injected into the telemetry stream one at a time. The problem is figuring out how to pull that stream of ones and zeros back apart on the ground. So every so often a known set of bits, specific pattern such as "fdc0f1hex" (nonsense number I just made up) is inserted into the stream so the ground decommutator can "pull" the data back apart and "read" the individual words. This known "word" is what is synced up on and is called the frame sync.
We can further sub-divide this telemetry stream into sub frames with a counter or a sub-frame sync to allow greater flexibility in how the parameters will be downlinked. Lets say we are doing something special, like running the robotic arm on the Shuttle. The telemetry stream has a finite space, so using a different set of sub-frames, we can downlink more data at that moment on the arm than our normal State-of-Health (SOH) telemetry monitors.
Rememer, there may be more than five thousand (5000) individual monitors that can be sent to the ground. The trick is, which ones and at what time during the mission should they be sent.
One of the largest data rates I ever worked with was 320 million bits/sec.
"Job security" others would answer
Actually one of the things that we were hoping to find was the Heliopause of our solar system.